The overall objective of the proposed in vitro studies is to measure proximal and distal load sharing between the radius and ulna, before and after surgical procedures designed to alter the load transmission pathway, and to identify ligamentous structures which are important in the load transfer process. Force measurements in the proximal radius and distal ulna will be performed on intact fresh-frozen forearm specimens mounted in a specially designed loading apparatus attached to a materials test machine. The basic experiment involves placing the wrist and elbow at fixed positions, applying a constant force to the forearm through the wrist, and recording the outputs of force transducers inserted into the distal ulna and proximal radius during manual rotation of the forearm from 65 degrees pronation to 65 degrees supination. A displacement transducer will be used to record relative axial motion between the radius and ulna at neutral forearm rotation. Four Specific Aims will be investigated: (1) the effects of forearm rotation, wrist flexion-extension, wrist deviation, elbow flexion, and elbow varus-valgus alignment will be studied for intact forearm specimens; (2) the role of the interconnecting ligaments upon load transfer between radius and ulna, and relative axial displacement between radius and ulna will be studied for fixed forearm and wrist positions at selected forearm rotation angles. Selective sectioning of the DRLC and IOM will be used to define the roles of these structures in forearm loading; (3) the effects of radial shortening upon measured forces in the distal ulna and proximal radius, and relative axial displacement between radius and ulna will be studied for fixed wrist and forearm positions at selected positions of forearm rotation. A slotted plate will be fixed to the radius and a transverse osteotomy will be performed; approximately 8 mm of bone will be removed. The original bone gap will be measured accurately with dial calipers, and radial shortenings of 2 mm, 4 mm and 6 mm will be created by re-fixing the plate to the radius; and (4) the effects of radial head excision and subsequent IOM section upon measured forces in the distal ulna, and relative axial displacement between radius and ulna will be studied for fixed wrist and forearm positions at selected positions of forearm rotation. Only 45 degrees of elbow flexion will be studied.